Generally, a fuel cell is mainly composed of an electrode for the electro-chemical reaction, an electrolyte film for transmitting a hydrogen ion generated by the reaction, and a bipolar plate for supporting the electrode and the electrolyte.
Since a high polymer electrolyte fuel has much higher efficiency as compared with other types of fuel cells. It also has a large current density, a large output density, a short start-up time, and uses a solid electrolyte. Corrosion and electrolyte adjustment are also not necessary for this fuel cell. Because it is an environment-friendly energy source which discharges the pure waters as an exhaust gas, automobile manufacturing companies the world over are now studying high polymer electrolyte fuel cells.
The high polymer electrolyte fuel cell generates water and heat through the electro-chemical reaction of hydrogen and oxygen. At the same time, it generates electricity, where the provided hydrogen is separated into hydrogen ions and electrons at the electrolyte of an anode electrode, and the separated hydrogen ions are transferred to a cathode via the electrolyte film. At this time, the provided oxygen and hydrogen ions are combined into electrons introduced from the exterior conduction lines. Water and electrical energy is generated. The generated theoretical electrical potential is about 1.23V and the reaction equation is as follows:Anode→H2- - - >2H++2e Cathode→½O2+2H++2e- - - >H2O
Actually, a fuel cell for vehicle requires a much higher potential than that mentioned above. Therefore, individual cells are piled-up to obtain a higher potential, and this is called as a stack.
An anode electrode and a cathode electrode are provided at the inner side of the stack, and in the case of start-up or shut-down of a fuel cell, the oxygen in the air is introduced into the stack, and a partial high voltage circuit is formed. Therefore, a drawback exists in that the carbon support material of the cathode side is corroded and disappears, significantly deteriorating the performance of the stack.